The Earth in the Universe - Earth, Stars, Galaxies and Space

The Earth is one of the eight planets orbiting the Sun, and there are many other members of the Solar System including asteroids, moons and planets. Data provides the answers to many questions on this subject, but some questions remain unanswered.

The Earth and the Universe

The Universe is considered to be everything there is, though most of it is thought to be empty. Much is now known about the Earth and the place of the Earth in the Universe, for example: the diameter of the Earth is 12,800km (7953 miles), the diameter of the Sun is 109 times that of the Earth's, the Earth is 150 million km (93 million miles) from the Sun and the distance to the nearest star is four light years.

The Solar System

The Earth is just one of the eight planets orbiting the Sun, which is a star. The orbits all lie in the same plane, and the planets all go round in the same direction. There are many other members of our Solar System: asteroids - much smaller than planets, and orbit the Sun. Most of the asteroids are between the planets Mars and Jupiter, but some come close to the Earth. Moons - orbit planets. Most are tiny. Only a few are as large as our moon, which is nearly a sixth of the diameter of the Earth. Comets - have different orbits to those of planets, spending much of their orbital time far from the Sun. Comets are similar in size to asteroid, but are made of dust and ice. The ice melts when the comet approches the Sun, and forms the comet's tail.

The Sun

Nearly all of the mass in our Solar System is in the Sun. The Sun is very large. Its diameter is 109 times the Earth's. The Sun is the source of nearly all the energy we recieve. For many years, it was a mystery as to where this came from and this baffled the leading scientists. It is now understood that the nuclear fusion is the energy source. In nuclear fusion, smaller nuclei came together and form larger nuclei. For example hydrogen nuclei are joined together to make helium nuclei. This release enormous amounts of energy. Hydrogen nucleus + hydrogen nucleus --> helium nuclei. In stars larger than our Sun, helium nuclei can be fused together to create larger atomic nuclei. As the Earth contains many of these larger atoms, like carbon, oxygen, iron, etc, scientists believe that our Solar System was made from the remains of an earlier star.

How Stars and Planets are formed

As the gas falls together, it gets hot. A star forms when it is hot enough for a nuclear fusion reaction to start. This releases energy, and keeps the star hot. The outward pressure from the expanding hot gases is balanced by the force of the star's gravity. This happened about 5 billion years ago. This is quite recent in the history of the Universe, which is currently…